RealtyTrac released today its Second Annual Manmade Environmental Hazards Housing Risk Report, which analyzed 7,751 ZIP codes throughout the nation and measured five environmental hazards: air quality, superfund sites, brownfields, former drug labs and polluters. RealtyTrac broke down the risk into five categories, ranging from very high to very low.

According to the report:

More than one-third of all U.S. single family homes and condos, or 25 million, are in ZIP codes at high risk or very high risk for manmade environmental hazards.

Home sales prices in ZIP codes with high risk are in 2015 are 15 percent lower compared to homes in ZIP codes with low risk

Home prices in high-risk ZIP codes are 1.8 percent lower on average than 10 years ago, while home prices in low-risk ZIP codes are 5.3 percent higher

In San Francisco County, zero ZIP codes are at high or very high risk. In the past 10 years, the median home sales price increased 45 percent.

“Buying a home in an area with low risk of manmade environmental hazards may not just be a good idea for health and safety reasons; it may also be good for financial reasons,” said Daren Blomquist, vice president at RealtyTrac, in a statement.

“Across the country, home prices in high risk zip codes were lower on average, and appreciation over the last 10 years slower when compared to home prices and 10-year appreciation in low risk zip codes.”